1. Field of the Invention
This invention relates to construction of a reinforced concrete structure. More specifically, the invention relates to a novel apparatus to be used in a method of manufacturing an arched concrete structure, such as an arched culvert or bridge or drainage line by applying a cementitious composition on a pressurized inflatable form which is confined by steel straps or related means.
2. Description of the Prior Art
The basic concept of manufacturing a reinforced concrete/shotcrete structure such as a building, pipe, or the like, is generally a well-established art. However, when attempting to employ this art, a combination of removable and reusable inflatable molds or forms, the available alternative methods of construction are plagued with problems that severely limit the commercial acceptance of such techniques. Yet in principle, a reliable and safe construction technique using an inflatable mold and concrete/shotcrete should lead to an extremely cost effective and structurally acceptable product.
Among the problems encountered in fabricating concrete on an inflatable form has been the tendency for the form to be displaced and distorted when heavy loads of cementatious compositions are applied to the form. These problems have been further complicated by the tendency of the inflatable form to vibrate and transmit relative movement during application and setting of the concrete. Various methods and techniques have been suggested and employed to compensate for such problems, particularly, when building large scale cement shell structures and the like. For example, in U.S. Pat. No. 2,388,701, a "workdown" procedure for cementing a hemispherical "open bottomed," inflatable form mounted on a circular foundation is disclosed. This "workdown" procedure involves applying the cement to the top third of the form first, thus creating a compression on the rest of the form. However, it is recognized in this patent that such a procedure induces significant distortion to the side walls of the domed form and resulting structure. This distortion problem is again acknowledged in U.S. Pat. No. 2,892,239 (apparently the same inventor) and compensated for by the use of a series of horizontal reinforced bands placed at the base of the domed top resting on vertically straight side walls of a circular structure. The straight side walls are also reinforced by bands of wire mesh wrapped around the available form and again the workdown procedure is viewed as critical to create the desired structural stress.
Other patents of interest include the U.S. Pat. No. 4,442,059, issued Apr. 10, 1984, to "Rigid Building Frame With Inflatable Member," Norman A. Boyce, inventor. This patent relates to the building of a domed building. U.S. Pat. No. 3,139,464, issued June 30, 1964, to W. W. Byrd et al entitled "Building Construction." U.S. Pat. No. 3,973,749, issued Aug. 10, 1976, to Franz Friadle, et al, and is entitled "Hollow Form Work Elements for Producing Concrete Structures," and relates to reusable hollow form work elements of elastic material which may be used for the concreting of pipelines.